The present invention relates to novel metallic dithiophosphates and their use as extreme-pressure and anti-wear additives for lubricating oils.
U.S. Pat. No. 3,944,495 discloses that automatic transmission fluids can be improved by the addition of metallic dithiophosphates of the formula: ##STR3## in which:
R represents a saturated C.sub.4 -C.sub.30 aliphatic radical;
R' represents hydrogen, a C.sub.1 -C.sub.6 alkyl radical, or a C.sub.6 -C.sub.9 aryl radical;
a is a whole number between 2 and 12;
n corresponds to the valence of the metal M; and
M represents an alkaline or alkaline-earth metal or a transition metal.
Such products are particularly well adapted to use in automatic transmission fluids, which do not require additives of great thermal stability.
On the other hand, such products are not sufficiently thermally stable to be used as additives for crankcase oils and, in particular, for crankcase diesel oils.
It is also known that the properties of lubricating oils can be improved, as disclosed in French Pat. No. 1,310,171 (U.S. counterpart, U.S. Pat. No. 3,102,096), by using metallic dialkyldithiophosphates prepared from monoalcohols of the "neo" type, that is to say, alcohols in which the carbon atom adjacent the carbon atom fixed to the hydroxyl group is fully replaced by alkyl groups. Such products have the drawback that they are of only average effectiveness and, furthermore, cannot be used industrially, due to the high cost of the "neo" monoalcohols.
By the present invention, new thermally stable metallic dithiophosphates have been discovered which can be used industrially in order, in particular, to improve the extreme-pressure and anti-wear properties of lubricating oils.
It is an object of the present invention to provide novel metallic dithiophosphates which improve the extreme-pressure and anti-wear properties of lubricating oils and which overcome the disadvantages of the prior art.
It is another object of the present invention to provide a novel process for the preparation of the metallic dithiophosphate oil additives of the invention.
It is a further object of the invention to provide novel lubricating oil compositions containing the metallic dithiophosphate additives of the invention.
Other objects will be apparent to those skilled in the art from the present description.